WO1990007787A1 - Contacteur a commande numerique et methode de commande de contacteur - Google Patents

Contacteur a commande numerique et methode de commande de contacteur Download PDF

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Publication number
WO1990007787A1
WO1990007787A1 PCT/FI1990/000003 FI9000003W WO9007787A1 WO 1990007787 A1 WO1990007787 A1 WO 1990007787A1 FI 9000003 W FI9000003 W FI 9000003W WO 9007787 A1 WO9007787 A1 WO 9007787A1
Authority
WO
WIPO (PCT)
Prior art keywords
contactor
coil
unit
voltage
control
Prior art date
Application number
PCT/FI1990/000003
Other languages
English (en)
Inventor
Petri Solanti
Hannu Tenhunen
Esko Kiiskinen
Original Assignee
Abb Strömberg Kojeet Oy
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Abb Strömberg Kojeet Oy filed Critical Abb Strömberg Kojeet Oy
Publication of WO1990007787A1 publication Critical patent/WO1990007787A1/fr

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H47/00—Circuit arrangements not adapted to a particular application of the relay and designed to obtain desired operating characteristics or to provide energising current
    • H01H47/22—Circuit arrangements not adapted to a particular application of the relay and designed to obtain desired operating characteristics or to provide energising current for supplying energising current for relay coil
    • H01H47/32—Energising current supplied by semiconductor device
    • H01H47/325—Energising current supplied by semiconductor device by switching regulator

Definitions

  • the present invention relates to an "intelligent" contact in accordance with the preamble of claim 1 for the connecti and disconnection of power at plants and loads .
  • the invention also concerns a method for controlling t connector.
  • the coil circuit is dimensioned operate over a very narrow range of voltage, and differe coil designs are needed for DC and AC operation, respe tively. Over a hundred various coil designs are required f a single contactor model.
  • the DC coils of larger contactors a complemented with auxiliary contacts used together with external series resistor in order to reduce the curre through the coil during the hold, thus achieving a lower temperature rise of the coil.
  • the mating surfaces of the - magnetic circuit in a direct actuated contactor are subjected to an unnecessarily hi stress, because during the closing stage the input power the coil is at a constant level, whereby the contact assemb tie reaches a relatively high final speed prior to t closure of the magnetic circuit. Since the power requir during the closing stage is higher than the power requir for holding the magnetic circuit closed, the closing co current must be designed to exceed the necessary holdi current by up to several ten-fold, depending on the contact model. Due to the overdimensioning, an increase of both pow consumption and heat load of the coil results. Aiming to overcome the aforementioned drawbacks, separat control units based on analog technology are used fo controlling the coil current.
  • the operating voltage range i the conventional control units is appreciably narrower tha that achievable with the apparatus disclosed herein, sinc analog technology is incapable of providing a sufficientl wide range of control.
  • the prior art devices ar expensive and large in size, while their implementatio technology limits the possibilities of increasing the numbe of functions available.
  • the aim of this invention is to overcome the disadvantages o prior-art methods described above and to achieve a novel typ of contactor and a method for controlling a contactor.
  • a control circuit in the context of this disclosure refers t a device, which is packaged into a single monolithic hybrid circuit, or onto a single printed-circuit board, a which performs the necessary control and steering functiono in the coil circuit of a contactor.
  • the invention is based on a control unit, which implemented in the digital technology, and attached to t coil circuit of the contactor, operates with pulse-wid modulation, having an integral power stage for the control the coil current.
  • the reference value of the coil current formed by way of a voltage signal obtained by measuring t control voltage of the coil.
  • the coil voltage is rectified and slightly iltered prior modulation, thereby allowing the apparatus to be used f both DC and AC control of a magnetic circuit designed for control, thus avoiding- the need for separate shading rin for the smoothing of the magnetic field.
  • the contactor in accordance with t invention is characterized by what is stated in t characterizing part of claim 1.
  • the invention provides outstanding technical and economica benefits over prior art technology.
  • the implementation in accordance with the invention achieve an accurate control of a contactor according to any prevalen conditions.
  • the magnetic circuit surfaces are relieved fro excessive closing stresses, and heat loads are reduced by th limitation of the hold power.
  • the control circuit is easily complemented b integrating additional functions into it as to be describe later.
  • Figure 1 shows a partially sectioned side view of a contacto in accordance with the invention.
  • Figure 2 shows in a graph the power required by the contacto coil as a function of time during the different stages of th closing of the contactor.
  • Figure 3 shows a block diagram of a possible embodiment fo the functional implementation of the control circuit.
  • Figure 4 shows the block diagram of a voltage measuring un in accordance with the invention.
  • FIG. 5 shows the block diagram of pulse-width modulat unit and power unit in accordance with the invention.
  • Figure 6 shows in a graph the adaptation of the pull force the contactor coil to the contact forces and the restorin spring forces as a function of force and opening gap of t magnetic circuit.
  • a digital control and steeri circuit 1 is connected between a coil circuit 3 of contactor 2 and a controlling line voltage 4.
  • the princip function of the control circuit is to control the curre passing through the coil 3 of the contactor 2 during t different stages of the contact closure (refer to Fig. 2) such a manner that unnecessary heating of the coil 3 avoided, yet assuring the closure of a magnetic circuit even in arduous environmental conditions such as stro vibration, for instance.
  • a contact assem tie 6 is closed and poles 7 are short-circuited by contactor 2.
  • the position of the tie 6 is monitored by me of a sensor 9.
  • the voltage of the controlling line 4 can v freely in the range 24 120 V or 120 450 V, while the f of the voltage can be DC or AC.
  • the control circuit receives the information necessary for controlling the c current from the voltage of the line 4 and the contac control information wired into the control circuit 1.
  • the circuit is provided w an I/O unit (not shown) , through which the communications the control circuit with the external environment ta place. The I/O unit will later be described in detail.
  • the design of the control circuit 1 pays special attention the operating conditions of contactors.
  • the contr circuit is provided with several monitoring and resetti facilities that are aimed to minimize the duration of a possible malfunction. Due to its susceptibility interference, a microcontroller in the control circuit h been discarded in the favour of discrete logic circuits which are divided into independently operating function blocks that are reset by a reset pulse obtained at se intervals from a timing unit.
  • the block' construction a timed resetting of the control circuit results in appreciably shorter recovery time than that obtainable with microcontroller-based structure, allowing in a favourabl case the malfunction to be confined to only a single bloc whereby the system function may remain unaffected.
  • the energy stored in the coil 3 i increased to assure the closure of the magnetic circuit 5 i all possible ambient conditions.
  • the third phase called the hold phase c is extended up to th next deactivation of the control signal.
  • the current of th coil 3 is limited during the hold phase to a level sufficie for maintaining the closure of the magnetic circuit, y avoiding the heating of the coil.
  • the functions of the control circuit 1 take into account so disturbance conditions, which can be cleared by a conve tional contactor only through the use of external component
  • One of most frequent situations is the quick reclosure of t supply after a short outage.
  • the control circuit 1 has state memory with a backup time of about one second from t loss of coil control voltage. If the contactor 2 w energized at the loss of coil voltage, the circuit initiates a start sequence in case the supply volta recovers within the backup time of the memory. After a long outage, the control circuit is latched to the "releas state, requiring the switch-off of all control signals pri to the next "operate" control signal.
  • the quick reclosu function can be disabled, whereafter even a momentary bre in the coil control voltage results in the resetting of t control circuit, and the contactor will stay nonenergiz until the next "operate” control signal. Consequently, t implementation of quick reclosure is possible without the u of external RC circuits that are required in convention systems.
  • the control circuit 1 incorporated with a delay for the control signals th inhibits the next "operate" control signal until the conta assembly tie can reach its upper position after the precedi "release” control signal.
  • the delay varies for differe types of contactors, but a typical value is less than 200 m
  • the circuit accepts the next control signal, but initiat the start sequence only after the set delay. Th characteristic is also valid for the quick reclosure. prior art systems the delay is implemented by way auxiliary contactors.
  • t contactor In accordance with a standard concerning contactors, t contactor must release during an undervoltage condition the range 20...75 % of nominal voltage in AC controll operation and in the range 10...75 % of nominal voltage in controlled operation.
  • the undervoltage monitoring function implemented in a voltage measuring unit 30, which issues t modulator unit an enabling "run" signal if the coil contr voltage is within allowed range limits.
  • the limit an undervoltage condition is set to within the ran expressed in the standard.
  • the control In an overvoltage condition the control is disabled when t control voltage exceeds by 15 % the upper limit (138 V f the voltage range 24...120 V and 517 V for the voltage ran 120...450 V) of allowable control voltage range of t control circuit.
  • the volta measuring unit For overvoltage monitoring the volta measuring unit is provided with two separate systems, which one detects transient voltage changes and the oth monitors the change of control voltage average value over longer span of time.- Tripping by under- and overvolta resets the control circuit, and recovery of voltages within allowable range does not energize the contactor prio to a new control signal.
  • Figure 3 illustrates the division of ASIC circuitry co taining the intelligence of the control system into fo functional blocks. All information transfer between t blocks is asynchronous to eliminate the effect disturbances. The inter aces and signals communicati externally from the blocks are to be defined later.
  • the functional blocks of the control circuit are:
  • Fig. 4 the measurement of the control voltage implemented with an A/D converter 40, based on sigma-del modulation and connected after a voltage divider circuit 4 feeding a digital averaging low-pass filter 41.
  • An alte native to the averaging filter is an integrating filte which could deliver an RMS value of higher accuracy, but th solution would consume more space on the silicon substra and the averaging function is suf iciently accurate in rel tion to the ambient conditions.
  • the S/D modulator (n shown) of the A/D converter 40 is capable of filtering t high- and medium-frequency interference from the measur signal, resulting in a 7-bit binary value, which after fi tration through the digital low-pass filter 41 represents t average value of the measured voltage.
  • the voltage inform tion is taken at appropriate intervals to the coding logic order to obtain a new set value for the modulation signa
  • the over- and undervoltage monitoring is implemented in detector 42 after the filtration, whereby possible distur ance transients in the supply line do not trigger an ove voltage trip.
  • the system is provided with a separate anal overvoltage monitoring, which is implemented with a volta reference 47 and a comparator 43.
  • a separate anal overvoltage monitoring which is implemented with a volta reference 47 and a comparator 43.
  • the output of the compara tor is routed via a delay line block 44, which prevents a overvoltage trip caused by fast transients (having a duratio of approx. 1...2 s) .
  • the delay line block issues the over voltage signal to the detector unit only when the comparato output has continuously been high for the duration set by th delay (approx. 1...2 ms) .
  • the detector unit will discontinu the "run" signal when it receives an "overvoltage” signal 4 from the delay line block, disregarding whether the averagin voltage measurement would indicate the line voltage to b within allowable limits.
  • the overvoltage limit is set accord ing to the maximum peak voltage U RM ⁇ ⁇ .. * 1.42 of the contro circuit in order to avoid tripping within an acceptabl voltage range.
  • the voltage measuring unit When the control circuit is connected to the coil suppl voltage, the voltage measuring unit first measures the coi circuit voltage via a measurement input 37 for about 20 ms i order to compute a definite value for the average voltage after which it sets the undervoltage limit and issues a "run enable signal to the modulator 31. If the coil supply voltag (coil control circuit voltage) is lower than a permanentl set- lower limit or higher than the overvoltage trip limit the "run" signal will not be issued.
  • the modulator unit comprises two majo blocks: a non- eedback digital pulse width modulato
  • NFBDPWM N-Fi Protected Access Memory
  • ROM circuit 51 which contains the store reference values of modulation for different types o contactors and voltages, complemented with the addres decoding logic of the memory.
  • the memory can be implemente using PROM, EPROM, EEPROM Flash-EEPROM or other memor circuit technology in an external block or designed integra with the circuitry.
  • the pulse-width modulator unit 31 is an independent unit wit internally synchronized function, whose only control signal are received from the voltage measuring unit 30 as t voltage information signal and the "run" signal, whi informs the modulator unit to set its operating state.
  • the pulse-width modulator 50 modulates the control pul signal routed to a drive unit 52 of the power switches. Th construction removes the instability and feedback-relat control errors typical to analog pulse-width modulators.
  • T modulator 50 resets itself after each control pulse and rea a new reference value of modulation from its latch circui
  • the latch circuit has a dual-part construction, whi facilitates its asynchronous setting and reading.
  • T modulator unit 31 is capable of controlling the pulse du cycle at 0.4 % accuracy over the range 0.4...98.4 %. Betwe each subsequent pulse remains a short gap, during which t new modulation data is read and the modulator is rese thereby making it impossible to use a full 100 % duty cyc of modulation. In comparison with corresponding anal implementations, the NFBDPWM approach offers an appreciab wide range of pulse-width duty cycle.
  • Pulse-width duty cycle values computed from tests for t hold power of contacts are programmed into the memory 51 a fetched therefrom by addresses decoded on the basis contactor control voltage and contactor type data, aft which they are latched into the latch circuit of t modulator.
  • the coils of different voltage ranges a dimensioned so as to avoid the need for separate memo blocks for them.
  • the power levels of the start sequence a obtained by adding a constant value determined by t contactor type to the value stored in the memory.
  • the memo can be organized, for instance, into 8 rows that a addressed by a 3-bit contactor type data 56, and into 1 columns that are addressed by 7-bit voltage information 5
  • Each memory cell contains 8-bit data of modulati information.
  • the actuator element of the control system is a switchi regulator implemented using a FET power switch that utiliz the contactor coil as its inductance element.
  • the FET swit is steered according to the contactor-type specif modulation information by the afore-described non-feedba digital pulse-width modulator (NFBDPWM) 50, which controlled by the voltage information signal obtained fr the voltage measuring unit 30.
  • the operating frequency of t switching regulator is above 20 kHz, whereby audib vibrations in the magnetic circuit 5 of the contactor 3 a avoided.
  • the modulator unit 31 does not incorporate a driver circu 52 of the FET switch, because the integration of the driv onto the same silicon chip with the logic control circuits impossible due to the difference in their operating volta ranges.
  • the FET switch is parallelled with an SA "snubbe circuit 54, whose function is to filter away the switchi transients imposed on the FET switch 53 and to reduce t switching losses of the FET.
  • the coil 3 is parallelled with protection diode 55, which absorbs the voltage spikes induc by the coil itself.
  • CMOS circuits The curren output capability of CMOS circuits is relatively low, and t 5 V supply voltage of the control logic circuits i insufficient for the drive voltage of the FET switch 53 whose gate voltage normally is in excess of 10 V.
  • a driver/isolator block is designe between the power switch block and the control circuit.
  • a timing unit 32 which delivers al timing signals required for the control circuit 1.
  • the clo generator of the timing unit 32 comprises a free-oscillati 5 MHz ring oscillator, whose output frequency is used as t basic frequency of the modulator.
  • the other timing signa are obtained by dividing the basic frequency and generati different sequences therefrom.
  • the different frequencies a required for, e.g., the voltage measuring unit 30 and the I units 33.
  • the timing unit 32 also generates the resetti signals required during the start sequence in a correct timed order for the different blocks.
  • the un incorporates a passive timer for the delaying of the contr signals and a short starting delay for duration of the clo generator startup.
  • An I/O unit 33 controls the operation of the control unit
  • the digital implementation of the I/O unit makes it feasib to integrate into the unit such functions that are possib in the conventional technology only through the use discrete equipment.
  • the I/O unit 33 concentrates all functions required for t control, communications, adjustments and internal diagnosti of the contactor.
  • the unit incorporates, for instance, thr different logic control signal connections, an interface f the serial-bus control, a programmable timer for setting t operate and release delays, a starting control logic f generating the commands to be delivered to the differe blocks during the start sequence in a correctly timed orde and an error-logging logic for collecting all reportab events occurring within the control circuit (such as malfunction, operation of thermal trip, etc.) and indicati these events by an LED indicator lamp and via an opt isolated open-collector output. All communications of the I unit to the other units takes place via a separate contr bus 36. The number of interchanged messages is minimized designing the units for maximum independence up to the internal diagnostics.
  • the only external connections n passing through the I/O unit are the measurement input of t voltage measuring unit and the outputs (2 pcs.) of the puls width modulator.
  • the connections of the I/O unit are lat designated by reference numbers 33a...33h.
  • the contactor operates at the rising edge of t control signal and releases at the falling edge. If t control signal is high when the coil voltage is applied, t contactor will not operate before the control signal is on taken low.
  • the automatic quick reclosure after a short outa maintains the state of the contactor prior to the break the memory and is activated when the control signal is high
  • a contact-closure signal input 33b has similar function wi the programmable-logic control input 33a; it is activate however, by a contact closure signal, rather than by voltage control signal.
  • This input can be controlled by relay, switch or open-collector logic output.
  • the contac closure control input is in parallel with the other input thereby allowing an active signal at any of the inputs operate the contactor.
  • a pulse-signal control input 33c is intended for mot controls and other similar applications, where the sta switch can be a pushbutton.
  • the contactor operates at a sho input pulse, after which it retains its state up to the ne voltage break or a reset pulse issued by a momentary cut-o of the PTC control signal.
  • the I/O unit has two resistance-measuring circuits 33d, whi can be used for connecting the PTC resistors applied to t temperature monitoring of the motor windings and bearing
  • the control circuit is reset and will not resta before the sensor resistance falls below the set limit val and all control signals are momentarily cut off. T activation of the thermal trip is alerted via the I/O unit a designated signal. The error message is retained in t memory until the next cut-off of coil voltage.
  • the I/O unit has a separate direct input 33e for electronic thermal trip.
  • This input connection is activat by a contact-closure signal, which disables the contact operation as long as the thermal trip contacts are open.
  • T connection can be used for direct routing of the thermal tr signal to the contactor, and the activation of the ther trip can be relayed via the contactor's error mess interface to an automatic control system.
  • the thermal t input can be disabled at will.
  • the I/O unit of the control circuit incorporates an interfa 33f for optical gap sensors that are used for monitoring t position and status of the contact assembly tie. Altern tively, magnetic sensors or microswitches, for instance, c be used as position sensors.
  • the position monitoring of t contact assembly serves for assuring a reliable conta closure and detecting a possible welding of the contacts contactor release.
  • the circuit When starting from a normal condition in which the conta assembly tie is in its upper position, the circuit initiat a start sequence. If the tie does not reach its low position at the end of the sequence, the circuit cuts off t coil voltage, waits for the return of the tie to its upp position and repeats the start attempt twice more. If ev the third attempt is unsuccessful, the I/O unit sets t error message flag and issues an alarm signal. The err message flag prevents the control circuit from functioni until its control voltage is cut off. If the contact assemb tie is not in its upper position at the beginning of t start sequence, the error message flag will be s immediately, thus preventing the initiation of the sta sequence.
  • the I/O unit has an integral timer, which can be used f delaying the operate time of the contactor after the issuan of the "operate" signal.
  • the operate delay is settable in t range 0.1...18 s or, alternatively, 1...180 s ( ⁇ 20 %) .
  • T release delay has an independent timer settable in the ran 0.1...18 s. The release delay is functional only conjunction with external control signals.
  • the control circuit 1 further includes a function, whi allows the heating of motor windings in humid environment f preventing condensation.
  • the control circuit in this ca carries on with the modulator function even after receivi the "release" control signal, but the modulator signal outp is routed to a designated output which feeds a separatel attached FET power switch with driver circuitry. T necessary heating power is precomputed, coded according the contactor type and stored in the memory of the modulat unit.
  • the internal diagnostics monitors the function of a internal circuit blocks of the control circuit and aims rectifying singular malfunctions.
  • the diagnostics al monitors the status of the power elements, and for the ca of power switch failure, the control circuit incorporates electronic fuse, which in a malfunction disconnects the co circuit.

Abstract

Contacteur (2) pour le branchement et le débranchement des installations et des utilisateurs aussi bien qu'une méthode de commande de contacteur. Ce dernier (2) comprend une structure (8); un circuit magnétique (5) constitué d'au moins deux parties (5) fixé à la structure (8) du contacteur; une bobine (3) fixée au circuit magnétique (5), ladite bobine permettant de fermer le circuit magnétique (5); des connecteurs de bobine (4) adaptés à la structure (8) et capables d'alimenter la bobine (3) en courant; des contacts de commutation de charge (7) adaptés à la structure (8) et capables d'assurer la commutation de puissance vers des installations reliées ou vers des utilisateurs; et un élément de liaison de contacteurs (6) faisant partie du circuit magnétique (5) et capable d'assurer le branchement désiré des contacts de commutation de charge (7). Dans la structure (8) ou dans une enceinte séparée que l'on peut fixer à la structure (8) se trouve un dispositif de commande numérique (1) de la bobine, vers lequel la tension d'alimentation est envoyée depuis les connecteurs de bobine (4), ledit dispositif comprenant une unité de mesure (3) de la tension de commande de la bobine, capable de mesurer la tension appliquée aux connecteurs de bobine (4); un modulateur (31) capable de fournir la modulation du courant de la bobine (3) à partir des valeurs de tension mesurées l'aide de l'unité de mesure de tension (30), une unité entrée/sortie, qui commande et surveille les jonctions du dispositif de commande et qui communique avec l'environnement extérieur; et une horloge (32) qui génère des signaux de synchronisation nécessaires à l'unité de mesure de tension de commande (30), au modulateur (31) et à l'unité entrée/sortie (33).
PCT/FI1990/000003 1988-12-30 1990-01-02 Contacteur a commande numerique et methode de commande de contacteur WO1990007787A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FI886063 1988-12-30
FI886063A FI81925C (fi) 1988-12-30 1988-12-30 Digitalt styrd kontaktor och foerfarande foer reglering av kontaktor.

Publications (1)

Publication Number Publication Date
WO1990007787A1 true WO1990007787A1 (fr) 1990-07-12

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PCT/FI1990/000003 WO1990007787A1 (fr) 1988-12-30 1990-01-02 Contacteur a commande numerique et methode de commande de contacteur

Country Status (4)

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EP (1) EP0402455A1 (fr)
AU (1) AU4816890A (fr)
FI (1) FI81925C (fr)
WO (1) WO1990007787A1 (fr)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0528357A2 (fr) * 1991-08-21 1993-02-24 Eaton Corporation Contrôleur pour un relais à temps d'attraction prédéterminé
US5662553A (en) * 1995-08-07 1997-09-02 Reichlinger; Gary Electromagnetic clutch and engine control
WO2002021885A2 (fr) * 2000-09-08 2002-03-14 Koninklijke Philips Electronics N.V. Systeme de protection contre les surtensions lors d'une gradation par modulation de largeur d'impulsion d'un onduleur de retroeclairage d'ecran lcd
US11183800B2 (en) 2018-08-29 2021-11-23 Leviton Manufacturing Co., Inc. Pin and sleeve device with indication
US11682889B2 (en) 2019-01-07 2023-06-20 Leviton Manufacturing Co., Inc. Electrical device with built-in sensors and/or communications

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4720761A (en) * 1987-02-19 1988-01-19 Westinghouse Electric Corp. Electromagnetic contactor with current regulated electromagnetic coil for holding the contacts closed

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4720761A (en) * 1987-02-19 1988-01-19 Westinghouse Electric Corp. Electromagnetic contactor with current regulated electromagnetic coil for holding the contacts closed

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0528357A2 (fr) * 1991-08-21 1993-02-24 Eaton Corporation Contrôleur pour un relais à temps d'attraction prédéterminé
EP0528357A3 (en) * 1991-08-21 1995-03-22 Eaton Corp Controller for fixed-time pull-in of a relay
US5662553A (en) * 1995-08-07 1997-09-02 Reichlinger; Gary Electromagnetic clutch and engine control
WO2002021885A2 (fr) * 2000-09-08 2002-03-14 Koninklijke Philips Electronics N.V. Systeme de protection contre les surtensions lors d'une gradation par modulation de largeur d'impulsion d'un onduleur de retroeclairage d'ecran lcd
WO2002021885A3 (fr) * 2000-09-08 2002-07-04 Koninkl Philips Electronics Nv Systeme de protection contre les surtensions lors d'une gradation par modulation de largeur d'impulsion d'un onduleur de retroeclairage d'ecran lcd
US11183800B2 (en) 2018-08-29 2021-11-23 Leviton Manufacturing Co., Inc. Pin and sleeve device with indication
US11682889B2 (en) 2019-01-07 2023-06-20 Leviton Manufacturing Co., Inc. Electrical device with built-in sensors and/or communications

Also Published As

Publication number Publication date
FI81925B (fi) 1990-08-31
FI81925C (fi) 1990-12-10
AU4816890A (en) 1990-08-01
EP0402455A1 (fr) 1990-12-19

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